C# - closures over class fields inside an initializer?
- by Richard Berg
Consider the following code:
using System;
namespace ConsoleApplication2
{
class Program
{
static void Main(string[] args)
{
var square = new Square(4);
Console.WriteLine(square.Calculate());
}
}
class MathOp
{
protected MathOp(Func<int> calc) { _calc = calc; }
public int Calculate() { return _calc(); }
private Func<int> _calc;
}
class Square : MathOp
{
public Square(int operand)
: base(() => _operand * _operand) // runtime exception
{
_operand = operand;
}
private int _operand;
}
}
(ignore the class design; I'm not actually writing a calculator! this code merely represents a minimal repro for a much bigger problem that took awhile to narrow down)
I would expect it to either:
print "16", OR
throw a compile time error if closing over a member field is not allowed in this scenario
Instead I get a nonsensical exception thrown at the indicated line. On the 3.0 CLR it's a NullReferenceException; on the Silverlight CLR it's the infamous Operation could destabilize the runtime.
